1. Field of the Invention
The present invention relates to a mold for injection molding, and an injection molding method, an injection-molded article, and an injection molding machine using the mold for injection molding.
2. Description of Related Art
As one of common techniques to remove an injection-molded article having an undercut portion from the mold, Japanese Patent Application Publication No. 2003-127183 (hereinafter referred to as “Patent literature 1”) discloses a slide-core technique. That is, as shown in FIG. 28 of the present application, Patent literature 1 discloses a mold for injection molding 103 including a stationary mold 100, a movable mold 101, and a slide core 102. The movable mold 101 can move in the vertical direction, and when the movable mold 101 is positioned at the highest position, the movable mold 101 engages with the stationary mold 100. The slide core 102 can move in the horizontal direction on the movable mold 101. This slide core 102 is equipped with a pin portion 106 that is used to form a hole 105 at one end of an injection-molded article 104. With this structure, by injecting a melted resin into the mold for injection molding 103 in a closed state, an injection-molded article 104 is formed. After the injection-molded article 104 is formed, by moving the movable mold 101 downward in the vertical direction, the mold for injection mold 103 is opened and the slide core 102 is moved backward in the horizontal direction by a guide rod (not shown) at the same time. In this way, the pin portion 106 is pulled away from the hole 105 of the injection-molded article 104, and the injection-molded article 104 can be thereby removed from the movable mold 101.
However, due to the recent trend of miniaturization of injection-molded articles, a possibility that physical interference occurs when an injection-molded article is removed from the mold for injection molding is increasing even for injection-molded articles in which no intentional undercut portion is provided unlike the above-described Patent literature 1. To explain this problem, a common structure of an injection molding machine and a mold for injection molding is shown hereinafter with reference to FIGS. 1 to 4.
[Injection Molding Machine 1]
As shown in FIG. 1, an injection molding machine 1 includes a machine pedestal 2. An injection unit 3 (melted-resin supply means), a mold clamping unit 4 (mold clamping means), and a mold for injection molding 5 are arranged on this machine pedestal 2.
The injection unit 3 includes a hopper 6 and a heating cylinder 7. The hopper 6 stores a resin that is used as raw material. The heating cylinder 7 heats the resin supplied from the hopper 6 and thereby transforms it into a melted resin. The melted resin formed inside the heating cylinder 7 is injected into a cavity 8 of the mold for injection molding 5 (also refer to FIG. 2).
The mold clamping unit 4 includes a stationary platen 9, a movable platen 10, a mold clamping drive unit 11, and an eject pin drive unit 12. A stationary-side mounting plate 13 of the mold for injection molding 5 is attached to the stationary platen 9 (also refer to FIG. 2). A movable-side mounting plate 14 of the mold for injection molding 5 is attached to the movable platen 10. The mold clamping drive unit 11 moves the movable platen 10 forward and backward with respect to the stationary platen 9, and thereby clamps and opens the mold for injection molding 5. The eject pin drive unit 12 moves an ejector plate 15 of the mold for injection molding 5 forward and backward.
[Mold for Injection Molding 5]
As shown in FIGS. 1 and 2, in the mold for injection molding 5, a stationary-side mounting plate 13, a stationary-side mold plate 16, a movable-side mold plate 17, a receiving plate 18, a spacer block 19, a movable-side mounting plate 14 are stacked on top of one another from the injection unit 3 side.
The stationary-side mounting plate 13 is attached to the stationary platen 9 of the mold clamping unit 4. A cavity 8 having a desired shape is formed between the stationary-side mold plate 16 and the movable-side mold plate 17. As shown in FIG. 2, in general, the stationary-side mold plate 16 and the movable-side mold plate 17 have a nesting structure. An injector plate 15 is housed inside the spacer block 19. The injector plate 15 is composed of an upper injector plate 20 and a lower injector plate 21. The injector plate 15 supports a plurality of injector pins 22. The movable-side mounting plate 14 is attached to the movable platen 10 of the mold clamping unit 4. Further, as shown in FIG. 2, a sprue 23, a runner 24, and a gate 25 are formed in the stationary-side mounting plate 13, the stationary-side mold plate 16, and the movable-side mold plate 17.
[Manufacturing Procedure of Injection-Molded Article 26]
In order to injection-mold an injection-molded article 26 like the one shown in FIG. 3 with the above-described structure, firstly, the mold for injection molding 5 is clamped by the mold clamping unit 4. As a result, as shown in FIG. 2, the sprue 23, the runner 24, the gate 25, and the cavity 8 are formed in the mold for injection molding 5. Next, a melted resin is injected into the mold for injection molding 5 by the injection unit 3. The melted resin injected from the injection unit 3 flows through the sprue 23, the runner 24, and the gate 25, and is charged into the cavity 8. Then, by cooling the mold for injection molding 5 by using cooling means (not shown), the melted resin charged in the cavity 8 is solidified.
After a predetermined time has elapsed from the start of the cooling, the mold for injection molding 5 is opened by the mold clamping unit 4. As a result, the injection-molded article 26, which is solidified and thereby formed in the cavity 8, is pulled away from the stationary-side mold plate 16 and is put into a state where the injection-molded article 26 is adhered to the inner wall surface of a recessed portion 27 of the movable-side mold plate 17 shown in FIG. 4. By moving the injector plate 15 forward by using the eject pin drive unit 12 in this state, the plurality of ejector pins 22 push out the injection-molded article 26 and the injection-molded article 26 is thereby removed from the movable-side mold plate 17.
[Place Where Problem Exists]
Next, an example of an FPC (Flexible Printed Circuit) connector 200 for use in a mobile phone is explained with reference to FIGS. 5, 6, and 7(a) to 7(e). Firstly, an example of the FPC connector 200 for use in a mobile phone is explained because the problem to be solved in the present application becomes particularly significant in extremely-small injection-molded articles such as a housing 201 of the FPC connector 200 for use in a mobile phone.
Now, as shown in FIG. 5, a large number of slits 202 are formed at regular intervals in the housing 201 of the FPC connector 200. Further, as shown in FIG. 6, a contact 203 is press-fitted in each of the slits 202. FIGS. 7(a) to 7(e) show a plane view, a front view, a bottom view, a left-side view, and a right-side view, respectively, of the housing 201 of the FPC connector 200. Supposing that the part of the housing 201 that is opposed to the gate 25 of the mold for injection molding 5, which is used to injection-mold the housing 201 of the FPC connector 200, is a part indicated by the symbol “G” in FIG. 7(d) (also refer to FIG. 4), the upper end face P1 in FIG. 7(a), the lower end face P2 in FIG. 7(c), and the side end face P3 in FIG. 7(e) correspond to the charging ends of the housing 201 at which a weld line is likely to appear.
Incidentally, there are cases in which a gas vent is formed on the inner wall surface at the charging end of the cavity 8 so that the air present in the cavity 8 before the charging and/or a gas generated from the melted resin are discharged to the outside and the melted resin is thereby smoothly charged into the cavity 8. A pin member (commonly called “gas discharge pin”) is usually inserted in this gas vent so that only the air and the gas are selectively discharged to the outside while preventing the melted resin from leaking from the cavity 8 to the outside. The end face of the pin member on the cavity 8 side is ground so that the end face becomes flush with the inner wall surface at the charging end of the cavity 8 as much as possible.
In principle, it can be arbitrarily determined which of the upper end face P1 in FIG. 7(a), the lower end face P2 in FIG. 7(c), and the side end face P3 in FIG. 7(e), the pin member for facilitating the charging is opposed to.
However, as shown in FIG. 7(a), a large number of slits 202 need to be formed on the upper surface 201UP of the housing 201 of the FPC connector 200, and in order to form these slits 202, a large number of core pins need to be provided on the stationary-side mold plate 16 that faces the upper surface 201UP of the housing 201 of the FPC connector 200 (also refer to FIG. 2). Therefore, there is no sufficient space on the inner wall surface of the stationary-side mold plate 16 facing the upper end face P1 shown in FIG. 7(a) to dispose the pin member for the above-described purpose.
Similarly, as shown in FIG. 7(c), a large number of core pins need to be provided on the movable-side mold plate 17 that faces the lower surface 201LW of the housing 201 of the FPC connector 200 (also refer to FIG. 2). Therefore, there is no sufficient space on the inner wall surface of the movable-side mold plate 17 facing the lower end face P2 shown in FIG. 7(c) to dispose the pin member for the above-described purpose.
Based on these reasons and based on the elimination method, only the inner wall surface of the movable-side mold plate 17 that faces the side end face P3 shown in FIG. 7(e) have a sufficient space to dispose the pin member for discharging the gas and/or detecting the charging.
Next, a problem to be solved in this application is explained in a more detailed manner with reference to FIGS. 8 to 11.
FIGS. 8 and 9 show an aspect in which a pin mounting hole 29 (corresponding to the above-described gas vent) is formed on a side-wall surface 28, which is the inner wall surface facing the side end face P3 shown in FIG. 7(e) among the inner wall surfaces of the cavity 8, and a pin member 30 is inserted and mounted in this pin mounting hole 29.
Then, as described previously, the end face 31 of the pin member 30 on the cavity 8 side (also refer to FIG. 2) is ground so that the end face becomes flush with the inner wall surface 28 of the cavity 8 as much as possible. However, theoretically speaking, it is naturally impossible to make the end face 31 of the pin member 30 on the cavity 8 side perfectly flush with the side-wall surface 28 of the cavity 8. For example, as shown in FIG. 8, the end 32 of the pin member 30 may protrude into the cavity 8. Alternatively, as shown in FIG. 9, a recessed portion 33 may be formed on the side-wall surface 28 of the cavity 8. Note that in FIGS. 8 and 9, the amount of the deviation of the end face 31 of the pin member 30 from the side-wall surface 28 of the cavity 8 is illustrated in a considerably-exaggerated fashion for the sake of explanation.
In practice, this deviation amount is about 50 micrometers at maximum. However, even such a small deviation amount could result in the following problems.
That is, FIG. 10 shows an injection-molded article 26 that is injection-molded by using the movable-side mold plate 17 shown in FIG. 8. As shown in FIG. 10, a recessed portion 35, with which the end 32 of the pin member 30 shown in FIG. 8 engages, is formed on an outer wall surface 34 of the injection-molded article 26. Therefore, when the injection-molded article 26 is removed from the movable-side mold plate 17, the injection-molded article 26 physically interferes with the end 32 of the pin member 30, and thereby making the removal of the injection-molded article 26 very difficult. Further, if the injection-molded article 26 is removed from the movable-side mold plate 17 against this physical interference by force, the end 32 of the pin member 30 is rubbed against the surface area 36 located on the opposite side in the mold-removal direction with respect to the recessed portion 35, and thereby causing a burr-like damage in the surface area 36. Further, this burr-like damage could generate shavings, and thereby possibly causing faulty connection when an FPC cable is connected with the FPC connector 200.
Further, FIG. 11 shows an injection-molded article 26 that is injection-molded by using the movable-side mold plate 17 shown in FIG. 9. As shown in FIG. 11, a protrusion 37, which engages with the recessed portion 33 of the side-wall surface 28 shown in FIG. 9, is formed on an outer wall surface 34 of the injection-molded article 26. Therefore, when the injection-molded article 26 is removed from the movable-side mold plate 17, the protrusion 37 of the injection-molded article 26 physically interferes with the movable-side mold plate 17, and thereby making the removal of the injection-molded article 26 very difficult. Further, if the injection-molded article 26 is removed from the movable-side mold plate 17 against this physical interference by force, the protrusion 37 of the injection-molded article 26 is forcibly pushed downward in the direction opposite to the mold-removal direction and thereby significantly deformed. Further, this significant deformation could cause shavings, and thereby possibly causing faulty connection when an FPC cable is connected with the FPC connector 200.
Accordingly, an object of the present invention is, in a mold for injection molding including a stationary-side mold plate and a movable-side mold plate, in which a cavity is formed between the stationary-side mold plate and the movable-side mold plate, and an injection-molded article is injection-molded by charging this cavity with a melted resin, to provide a technique to remove the injection-molded article from the mold for injection molding without problems even when there is a pin member that is otherwise likely to prevent the injection-molded article from being smoothly removed.